Weird problem, timing related
Thread Starter
On The Tree
Joined: Feb 2004
Posts: 156
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From: Fayetteville, NC
Weird problem, timing related Ok guys, I got my car dyno tuned today for my H/C. Something very strange is happening that is affecting my low rpm, full throttle timing (hell, part throttle too!). In the log on HPTuners is seems to be MAF related, but we switched meters, & the problem was still there.
The tuner would start the pull at 1800 rpm in 4th (of course), & the MAF readings would fluctuate wildly, which would cause the timing to be retarded to 16.5 total. This would happen until 2500+- when it would straighten up, & the run would go flawlessly. No matter what he tried, he couldn't get it to stop doing this. We made 7 runs, & it repeated itself, identically, every time. Once I get a picture or a scan of the dyno graph, you can see it.
This is of course effecting my in town driving. Sluggish isn't a strong enough word to describe low rpms. You can actually feel when the timing goes back up. It almost feels like a small shot of nitrous, that's how dramatic it is. I feel like I'm driving a 4cyl. that sounds like a V8, in low rpms.
He worked on it for hours, but we ran out of time today. He said that he would continue researching it, but I thought I would do some of my own. Peak numbers were low, because whats the point in tuning for max hp, when low rpms are so screwed up. This looks to be the begining stages of doing my own tuning. Might as well start learning about this stuff now.
IDEAS??
The tuner would start the pull at 1800 rpm in 4th (of course), & the MAF readings would fluctuate wildly, which would cause the timing to be retarded to 16.5 total. This would happen until 2500+- when it would straighten up, & the run would go flawlessly. No matter what he tried, he couldn't get it to stop doing this. We made 7 runs, & it repeated itself, identically, every time. Once I get a picture or a scan of the dyno graph, you can see it.
This is of course effecting my in town driving. Sluggish isn't a strong enough word to describe low rpms. You can actually feel when the timing goes back up. It almost feels like a small shot of nitrous, that's how dramatic it is. I feel like I'm driving a 4cyl. that sounds like a V8, in low rpms.
He worked on it for hours, but we ran out of time today. He said that he would continue researching it, but I thought I would do some of my own. Peak numbers were low, because whats the point in tuning for max hp, when low rpms are so screwed up. This looks to be the begining stages of doing my own tuning. Might as well start learning about this stuff now.
IDEAS??
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
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From: Lake Zurich, IL
when i had a broken valve spring I would notice some reversion thorugh the MAF... it'd read high then low then go back up then drop down... You sure hte valve springs are all good and aren't tired?
Thread Starter
On The Tree
Joined: Feb 2004
Posts: 156
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From: Fayetteville, NC
Originally Posted by horist
when i had a broken valve spring I would notice some reversion thorugh the MAF... it'd read high then low then go back up then drop down... You sure hte valve springs are all good and aren't tired?
Shouldn't be that. I'm running PRC gold duals with less than 150 miles on them now. I can pull my covers & check, but it's only in low rpms. After 2500, it runs GREAT.
He also couldn't manage to get the idle dailed in, which he said he's never had a problem with.
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
could possibly be because of the cam... lower RPMs you're going to have alot of time when both valves are open which would cause air to push back out... higher RPMs it's not as big of an issue...
Looks like you must be a 6 speed car? If so I'm not sure if that's normal or not... my car hasn't seen below 4500 or so RPMs on a dyno in a while... never seen a car dynoed WOT at such a low RPM
Looks like you must be a 6 speed car? If so I'm not sure if that's normal or not... my car hasn't seen below 4500 or so RPMs on a dyno in a while... never seen a car dynoed WOT at such a low RPM
Thread Starter
On The Tree
Joined: Feb 2004
Posts: 156
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From: Fayetteville, NC
Originally Posted by horist
Looks like you must be a 6 speed car? If so I'm not sure if that's normal or not... my car hasn't seen below 4500 or so RPMs on a dyno in a while... never seen a car dynoed WOT at such a low RPM
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Verdad Gallardo Thread Starter
On The Tree
Joined: Feb 2004
Posts: 156
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From: Fayetteville, NC
Originally Posted by RedHardSupra
on a vette you gotta disable it from software, as you have an integrated iat/maf plug. just set 'maf fail frequency' to 0 and off you go in speed density.
Sounds like the MAF is OK (noise aside) and the
speed density tune is what's bent, like nobody
did the job after heads, cam, hello? Other things
could be bugging the MAF down low but it's being
mostly ignored anyway, there. Once you get up
to where the MAF matters, things get better.
Like a crutch is better than a broken leg.
speed density tune is what's bent, like nobody
did the job after heads, cam, hello? Other things
could be bugging the MAF down low but it's being
mostly ignored anyway, there. Once you get up
to where the MAF matters, things get better.
Like a crutch is better than a broken leg.
Thread Starter
On The Tree
Joined: Feb 2004
Posts: 156
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From: Fayetteville, NC
Originally Posted by RedHardSupra
if your tuner doesn't know that, you don't let him know, you fire him.
Well, I'm not sure if had tried that yet, what I sould've said is I'll ask him if he has done that. I have total confidence in him to make it right.
TECH Fanatic
Joined: Mar 2003
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Originally Posted by RedHardSupra
on a vette you gotta disable it from software, as you have an integrated iat/maf plug. just set 'maf fail frequency' to 0 and off you go in speed density.
Originally Posted by jimmyblue
Once you get up
to where the MAF matters, things get better.
Like a crutch is better than a broken leg.
to where the MAF matters, things get better.
Like a crutch is better than a broken leg.
Thread Starter
On The Tree
Joined: Feb 2004
Posts: 156
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From: Fayetteville, NC
Still trying to find the problem.
http://forums.corvetteforum.com/show...13&forum_id=91
No codes since the tune, before I was getting random cylinder misfire, but no MAF related codes. He has absolutely tuned other vettes. Just recently a triple black very w/ a 408, & a much bigger cam than mine.
"Did you try copying your High Octane table to the Low Octane Table - which would give you 25 - 29 * of commanded Spark?" He specifically mentioned doing this, with no change before 2750 rpm, it still only shows 14* timing.
Running it in SD mode clears it up. With the MAF connected, the weird thing is, that no matter what he does, & he assures me he has tried everything, it will not get over 14* of timing before 2750 rpm, EVERYTIME.
Another thing that just started is that the dash will randomly quit. It did it twice last week. No lights, no gauge sweep, the DIC doesn't work, press the traction control button = nothing, the door ajar chime doesn't work, etc... Disconnect the battery, & it starts working again. THe car will turn on, but the gauges don't work, it's weird. Could this be a ground, or BCM PCM issue?
I don't have a scan of the MAF readings, but here is the dyno graph. Check it out before 2750.
http://forums.corvetteforum.com/show...13&forum_id=91
No codes since the tune, before I was getting random cylinder misfire, but no MAF related codes. He has absolutely tuned other vettes. Just recently a triple black very w/ a 408, & a much bigger cam than mine.
"Did you try copying your High Octane table to the Low Octane Table - which would give you 25 - 29 * of commanded Spark?" He specifically mentioned doing this, with no change before 2750 rpm, it still only shows 14* timing.
Running it in SD mode clears it up. With the MAF connected, the weird thing is, that no matter what he does, & he assures me he has tried everything, it will not get over 14* of timing before 2750 rpm, EVERYTIME.
Another thing that just started is that the dash will randomly quit. It did it twice last week. No lights, no gauge sweep, the DIC doesn't work, press the traction control button = nothing, the door ajar chime doesn't work, etc... Disconnect the battery, & it starts working again. THe car will turn on, but the gauges don't work, it's weird. Could this be a ground, or BCM PCM issue?
I don't have a scan of the MAF readings, but here is the dyno graph. Check it out before 2750.
2 things:
1. if SD works fine but with MAF it screws up, it means MAF is simply miscalibrated. MAF readings change DRAMATICALLY down low, sometimes as much as 100% of initial values.
2. idle spark in drive: in the really low rpm/tps areas the spark is dictated by the 'idle spark in drive' (i assume you got a stick) tables, not by the main HI/LO spark tables. the trick here is that with different vacuum (courtesy of h/c) the area from which the values would be set are gonna be completely different, that's why you'd get 14 when you need more like 30 degs of timing.
1. if SD works fine but with MAF it screws up, it means MAF is simply miscalibrated. MAF readings change DRAMATICALLY down low, sometimes as much as 100% of initial values.
2. idle spark in drive: in the really low rpm/tps areas the spark is dictated by the 'idle spark in drive' (i assume you got a stick) tables, not by the main HI/LO spark tables. the trick here is that with different vacuum (courtesy of h/c) the area from which the values would be set are gonna be completely different, that's why you'd get 14 when you need more like 30 degs of timing.
Thread Starter
On The Tree
Joined: Feb 2004
Posts: 156
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From: Fayetteville, NC
Originally Posted by RedHardSupra
2 things:
1. if SD works fine but with MAF it screws up, it means MAF is simply miscalibrated. MAF readings change DRAMATICALLY down low, sometimes as much as 100% of initial values.
2. idle spark in drive: in the really low rpm/tps areas the spark is dictated by the 'idle spark in drive' (i assume you got a stick) tables, not by the main HI/LO spark tables. the trick here is that with different vacuum (courtesy of h/c) the area from which the values would be set are gonna be completely different, that's why you'd get 14 when you need more like 30 degs of timing.
1. if SD works fine but with MAF it screws up, it means MAF is simply miscalibrated. MAF readings change DRAMATICALLY down low, sometimes as much as 100% of initial values.
2. idle spark in drive: in the really low rpm/tps areas the spark is dictated by the 'idle spark in drive' (i assume you got a stick) tables, not by the main HI/LO spark tables. the trick here is that with different vacuum (courtesy of h/c) the area from which the values would be set are gonna be completely different, that's why you'd get 14 when you need more like 30 degs of timing.
MAF's wont change ****, it's all in the tune. if your 'tuner' doesn't know this, i'd highly recommend finding a better one. If they don't know how to identifiy the source of the problem between VE and MAF tables, i'd be weary of their claims of expertise.
another thing possibly screwing with you (even though it's unlikely, as i never seen it happen with this cam) is reversion throwing off maf, no matter how well tuned it would be.
do you have a bin or at least some tables (screenshots?) of your settings?
another thing possibly screwing with you (even though it's unlikely, as i never seen it happen with this cam) is reversion throwing off maf, no matter how well tuned it would be.
do you have a bin or at least some tables (screenshots?) of your settings?